Telecommunications companies have the responsibility of providing reliable communication services that today's society critically depends on in its daily activities. To minimize potential service interruptions, reserve power systems have become standard industrial practice in the telecommunications companies' efforts to maintain extremely high network reliability and availability. In keeping with this notion, subscribers have come to view communication services as a basic and vital utility in similar light as electricity; thus, any disruption of service would substantially impair productivity and cause undue incovenience. These services include basic telephone and data communication services for transacting business and satisfying personal needs.
To provide these essential services, communication providers rely on their outside plant facilities in reaching the subscribers. The outside plant encompasses all physical cable and electronics required to connect customers to the switching equipment in the Central Offices. As digital communications and its applications (e.g., video teleconferencing, Internet access, data network connectivity, etc.) become more prevalent, the demand on the telecommunications companies' outside plant will be much greater in terms of deployment of fiber optic cables and related equipment. This equipment, however, draws greater power than the familiar copper wire technology, and thereby, necessitates a higher capacity back-up power.
To meet the demand for uninterrupted service, telecommunications companies have traditionally utilized batteries as the reserve power system to curb potential power disruptions. The Valve Regulated Lead Acid (VRLA) battery represents a popular reserve power system for today's outside plant. VRLA batteries allow sustained telephone service capability for some duration of outage of normal power, so that a technician can be dispatched to restore the power. However, this duration varies unpredictably at times. With the sophistication of the evolving outside plant facilities, larger and thus heavier batteries are required.
Unfortunately, battery systems possess a number of technical and operational drawbacks with respect to network performance, reliability, and cost. Because of the variable environmental conditions (e.g., extreme temperatures) of the outside plant, batteries suffer from a relatively short life and require substantial routine maintenance. Battery life is reduced by heat degradation, which may result in a decreased life by as much as 50 percent. Low temperature also adversely affects the storage capacity of batteries.
In addition, the shortened battery life can be attributed to the fact that batteries undergo frequent deep discharging and recharging. Discharging occurs when the back-up power is triggered and supplies power to the active network equipment. At times, this discharging of the battery continues for a significant duration until service of the AC mains generator power is restored. Once restored, the battery undergoes a recharging process. The continual cycle of discharging and recharging eventually degenerates the battery's full capacity--an inherent characteristic of electrochemical processes.
Also, because power disruptions occur quite frequently in short spurts, the batteries are discharged and recharged repeatedly for brief periods. This causes the batteries to experience "memory" effects, a phenomenon whereby battery capacity is reduced because the battery is not fully discharged before recharging. When a fully charged battery discharges for a short duration, it "remembers" the recharge cycle time and recharges only for this shortened duration even if the battery has not been fully recharged. "Memory" effects are more pronounced in certain combination of metals and electrolytes than other usually more expensive combinations of metals and electrolytic solutions.
The consequence of having so many variable factors bearing on battery life is that life cycle costs cannot be predicted reliably. For example, a battery projected to be replaced every five years may in fact have to be replaced at shorter intervals than projected; e.g., three years. Frequent battery replacement imposes significant costs for the replacement units and associated labor.
Another drawback of the battery system concerns inadequate monitoring capabilities. The ability to monitor battery back-up power systems is severely limited to "dumb" information. That is, no information can be gathered on the batteries' life, amount of stored energy, or environmental temperature other than total system failure. Hence, prediction of its maintenance and replacement cycle is problematic. Because of the lack of "intelligent" monitoring capability, these battery systems require continuous on-site maintenance and manual monitoring, which detrimentally impacts operational costs.
A further disadvantage is that batteries pose severe environmental hazards due to leakage and disposal. For instance, under certain conditions, the batteries may release explosive hydrogen gas.
As an effective alternative for reserved power systems, flywheel energy storage systems (FESS) have been explored in a few esoteric applications. Eisenhaure et al. (U.S. Pat. No. 4,617,507) describes a self-regulating energy storage system involving a flywheel attached to a motor/generator. The flywheel stores energy during surplus power conditions and returns it to the motor/generator during low power conditions. Eisenhaure further discloses the application of this energy storage system in satellite systems. The Nola Patent (U.S. Pat. No. 4,649,287) discusses the use of a FESS in a spacecraft. Essentially, the flywheel operates a motor as a generator when solar energy power is unavailable.
There have been suggestions to use flywheel power in land based communication networks, but actual systems have not been developed to provide power for specific types of outside plant equipment. The high level suggestions, for example, have not addressed specific optical terminal system power or how to automatically monitor and manage reserve power systems in the outside plant. On the whole, these suggestions aim to effect industry standards for flywheel systems' specification in communications networks--employing ONUs, fiber-to-the-home (FTTH), fiber-to-the-curb (FTTC), and digital loop carrier (DLC) systems--without regard to detailed implementation.
It is thus evident that little or no work has been done to fully integrate flywheel technology into modern fiber optic based communication networks.
Accordingly, there exists a need for a practical back-up power system that is intelligently managed, predictable, relatively light weight, and specifically adapted to wide scale use in the outside plant of communication networks.
A void exists to better minimize the power interruptions that inheres in outside plant power.
There is a need to more efficiently maintain service capability during power failures.
A need exists for a reserve power system which will facilitate implementation of fiber optic technology down to the subscribers.
A reserve power system is needed that can more quickly recharge and is free from life shortening phenomena such as memory effects as well as temperature and discharging/recharging induced degradations.
In addition, there exists a need to utilize environmentally safe reserved power systems.